function xstCOMFn = stCOMFn(x)
xstCOMFn = (12759122123*sin(x(1)) + 14065902578*sin(x(1) + x(2)) -  ...
  1637194622*sin(x(1) + x(2) + x(3)) -  ...
  457593477*sin(x(1) + x(2) + x(3) - x(4)))/(-12759122123*cos(x(1)) -  ...
  14065902578*cos(x(1) + x(2)) + 1637194622*cos(x(1) + x(2) + x(3)) +  ...
  457593477*cos(x(1) + x(2) + x(3) - x(4))) ...
;